Hirth HM 500

The Hirth HM 500 was a German four-cylinder air-cooled inverted inline engine developed from the Hirth HM 504 in 1938. Although developing the same output of the HM 504 (105 hp) and keeping the same capacity and bore, the HM 500 was a very different engine; the new HM 500 had a one-piece "closed" crankcase[1] for simplified manufacture.[2] The new cooling system reduced cylinder temperatures considerably (15 °C less), and the fuel consumption was also reduced. The HM 500 carried a twin-magneto instead of the two separate magnetos as on the old HM 504. All these changes made that the HM 500 resulted a 12% lighter than the HM 504 and the front surface 37% less than the previous HM 504.[3]

HM 500
Hirth HM 500
Type Inline piston engine
National origin Germany
Manufacturer Hirth
First run 1938
Major applications Bücker Bü 181
Unit cost 3129.42 RM (core)
Developed from Hirth HM 504

Otherwise the HM 500 continued the typical Hirth use of built-up crankshafts and roller-bearings for crankshaft & connecting rods (Hirth patents) as well as magnesium-alloy crankcases which made Hirth engines so popular in the 1930s.

Due to low fuel consumption and excellent reliability, the HM 500 was chosen as the powerplant for the Bücker Bü 181.


Specifications (HM 500A)

General characteristics

  • Type: 4-cylinder air-cooled inverted inline
  • Bore: 105 mm (4.134 in.)
  • Stroke: 115 mm (4.528 in.)
  • Displacement: 3983 cm3 (243.1 cuin)
  • Length: 978 mm
  • Width: 420 mm
  • Height: 665 mm
  • Dry weight: 91.50 kg (core)


  • Valvetrain: 1 inlet and 1 exhaust valve per cylinder
  • Fuel type: A3 (80 octane)
  • Cooling system: air


  • Power output: 105 hp at 2500 RPM
  • Compression ratio: 6:1
  • Fuel consumption: 210 -230 gr /PSh
  • Oil consumption: 3g /PSh

See also

Comparable engines

Related lists



  1. The HM 504 had a three part crankcase
  2. The time consumed to build an engine passed from an average 1775 minutes on the HM 504 to 945 minutes with the new HM 500
  3. Flugmotor Hirth HM 500, Luftfahrt International Nr 6, Dec. 1974


  • Der Hirth Flugmotor HM 500, 1944
  • Die Entwicklung der Hirth-Motoren, 1942
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